The present invention relates to the catalytic hydrodesulfurization of ortho-aminobenzyl sulfides to obtain ortho-alkylanilines, and in particular such reactions of 3-trifluoromethyl-2-aminobenzyl sulfides to obtain 2-trifluoromethyl-6-methylaniline.
A number of publications have disclosed methods for the desulfurization of organic sulfur compounds. For example, catalytic hydrogenation at temperatures usually between 623.15.degree. K. (350.degree. C.) and 723.15.degree. K. (450.degree. C.) in the presence of various metals, metallic oxides or sulfides has been used in the petroleum industry to convert the organically combined sulfur in petroleum fractions into hydrogen sulfide, see Berkman et al., Catalysis, Reinhold Publishing Corp., New York, 1940, pp. 925-930. The principle chemical reaction in petroleum fraction hydrodesulfurization is essentially limited to the rupture of simple carbon-sulfur bonds with saturation of olefinic double bonds and aromatic ring structures. In addition, the petroleum industry methods result in a certain amount of denitrification of reactant compounds. The petroleum industry method is unsuitable to promote the class of reactions contemplated by the present invention due to the highly functional substituents present on the orthoaminobenzyl sulfide reactants. In the reactions of the present invention it is desired that the aromatic structure with the substituent groups be retained while cleaving the carbon-sulfur bond to obtain the corresponding substituted aniline. Furthermore, the substituted ortho-aminobenzyl sulfides are generally unstable at the operating temperatures of the petroleum industry method.
Desulfurization by heating with a relatively large amount of Raney nickel has become a useful method in laboratory and small-scale organic synthesis. The principle disadvantages of the Raney nickel method are the large amount of nickel required, commonly three to fifty times the weight of organic reactant, difficulty in isolating products which are adsorbed onto the nickel, and the pyrophoric nature of the reagent. The above mentioned disadvantages make the Raney nickel method unattractive for large scale commercial processes.
While reports of prior work in catalytic hydrodesulfurization of organic substrates outside petroleum processing have been somewhat limited, at least one report in this area taught away from and, as a practical matter, discouraged the low temperature catalytic hydrodesulfurization process of the present invention. See A. C. Cope et al., "Cleavage of Carbon-Sulfur Bonds by Catalytic Hydrodesulfurization", J. Org. Chem.,19, 385 (1954) wherein it was reported that hydrogenation of simple mercaptans such as tert-octyl mercaptan was erratic at 513.15.degree. K. (240.degree. C.) using a commercial cobalt molybdenum catalyst and the inability to hydrogenate a simple sulfide (heptyl sulfide) at 533.15.degree. K. (260.degree. C.) using a commercial cobalt molybdenum catalyst.
It is the overall object of the present invention to provide a process for the catalytic hydrodesulfurization of ortho-aminobenzyl sulfides to obtain ortho-alkylanilines.
It is an object of the present invention to provide a process which is capable of desulfurizing the highly functionalized organic sulfides contemplated by this invention while not substantially effecting substituents present in the organic sulfide reactant.
It is, therefore, another object of the present invention to provide a hydrodesulfurization process capable of operating at mild reaction conditions relative to processes disclosed heretofore.
It is still another object of the present invention to provide a process capable of operating at high concentrations of the organic sulfide reactant to achieve practical payloads.
These and other objects, features, and advantages of the present invention will be evident to one skilled in the art from the following description and examples.